Photon Correlation Spectroscopy (PCS) will be used to monitor diffusion and polydispersity in solutions of HbS through the gel transition. Infrared radiation will be used to reduce the absorption of the samples. The elastic properties of the gels will also be investigated using the light scattering method developed by R. Nossal. These measurements will be complemented by NMR measurements using the pulsed field gradient method. Tracer diffusion will be monitored by this technique and an attempt will be made to study HbS mobility inside red cells.